Radio device



Patented Feb. 28,1933

- NEIL,R..COLLINS, ,o'r annwooncrrir, cALIro'RNInQ assrenoaro immune COMPANY, OEiSAN r mncrsco, cAnIroRnrA. AconroRA'rIoN OF CALIFORNIA. I e

RADIO nnvfcj: e

mi Drawing.

This invention hastodo the preparation of electron-emitting cathodes for use in thermionic discharge devices such .1 as threeelectrode vacuum tubes and the like.

The invention relates more particularly to a methodof applyingelectron-emitting ox-,

idecoatings and to a novel coating composi-v tion. I

The primary object of this inventionis to produce a filament or other form of electronemitting cathode characterized by high elecsecondary object is to devise a practicable and economical method of producing cathare believed to be novel.

According to the preferred practice a cathode coating preparation is made as follows:

Approximately equal parts by weight of barium and strontium iodides are placed in a porcelain crucible, together with avery smallportion, say, 0.5 per cent of barium hydroxide. Heat is then applied to the crucible and the water of crystallization thereby driven off. The temperature is then further raised until a quiet fusion takes place. This temperature is doubtless not above 800 C.,

since decomposition takes place near that;

point. As soon as the melt has reached a condition of quiet fusion it is poured into a warm mould and [cast into pencils. These.

pencils consist probably of an homogeneous mixture of the fused iodides, although it may possibly be that some-other chemical combinations are formed,

The filament core to be coated, whichconsistspreferably of a ribbon or wire of platinum or platinum-iridium alloy, is stretched between two metalliccontacts and sufficient current passed through to bring it to a dull -App1ic ation' filed i l'ulyw5, 1929} Serial 1%. 378,289. g 7

,red heat While the current is still on, a pencil prepared as above describedzisrubbed part of. the pencil'ewith which it makes contact. V The molten coating covers the wire or ribbon: uniformly; and rapidly solidifies.

VVith the filament at red heat decomposition filamenta coating which is presumed to consist mainly of amixture of the oxides of batronic emissivity and long emission life. A

rium and strontium. The a decomposition is apparently complete-but any residue of iodide which may remain, is subsequently decomposed duringtheevacuating process. i

1 Unless the coated filament isto be mounted immediately and the device in which it is to be incorporated is tobe p'romptlyevacuated it is preferable, if not essential, that it begiven' an additional protective coating 9 adaptedtoprotect it against moisture. 1A coatingof paraffin is suitable for this :purpose. #The 'oxidesof. both barium and strontiumare quite deliquescent, and consequently if the coated filaments are left exposed to the atmosphere without a protective coating for a substantial length of time the oxides will become converted tothe hydroxides to an objectionable extent.

Itwas hereinbefore stated that asmall portion of barium hydroxide is preferably included in, the coating mixture. The reason for including this compound is that it has a desirable effect on the surface of the platinumor platinum-iridium alloy of which the filament core is preferably composed. The

barium hydroxide, apparently attacks and slightly roughens the metallic surface, thereby promoting adhesion of the oxide coating.

A substantial amount of hydroxide inthe coating-mixture is objectionable for reasons unrelatedrto that which prompts its. use in small proportions as above stated. l I

d 'When the filament isheated during ;the

process of evacuation of the device in which it is used, the barium hydroxide asF well as any residual iodides which may. have rec It is not essential thatequalparts of stronoccurs very rapidly, thereby leavingon the vmained are converted completely into oxides.

tium and bariumfiodides be used in making with well known evacuation and getterin processes-the" filament or other form o cathode being raised preferably to a rather high temperature during evacuation and gettering so as to remove as far as possible all objectionable occluded gases. It is during i this step in the process of manufacture that ticular composition of matter has been specified there are obvious equivalents which will and appl ing to the oxide coated cathode thus produced a temporary moisture proof fusible coating. 1

In testimony whereof, I have hereunto set my hand.

' NEIL R. COLLINS.

any'residua-liodides or hydroxide in the coatin material becomes convertedto the oxides. it is manifest that although only one par-' immediately suggest themselves to those skilled in the art, and it is contemplated that those equivalents are embraced Within the scope and spirit of this invention.

Since thermionically active elements are most commonly used as cathodes in vacuum tube devices, the claims define the body to be coated as a cathode. However, it is conceivable that electronemitting bodies may be used under such conditions that they do not form cathodes and, therefore, the term cathode .as used in the claims is intended to apply to any electron emitting element, however used.

What is claimed is;

' 1. A coating preparation for electron-emitting cathodes comprising a halogen compound of alkaline-earth metal, together with a predetermined proportion of a hydroxide.

2. A coating preparation for electronemitting cathodes comprising barium iodide,

strontium iodide, and a small proportion of barium hydroxide.

3. The process in the-manufacture of oxide coated cathodes which comprises melting a mixture of halogen compounds of different alkaline-earth metals, and heating the same until it reaches a state of; quite fusion, allowing the fused mixtureto cooland thereafter o rubbing the same on a heated cathode core,'

thereby applying thereto an adherent coating, and thereafter raisingthe, temperature of the coated core sufliciently tdconvert the coating thereon completely, or substantially so, to the oxide form.

4. The process in the manufacture o f oxide coated cathodes which comprises melting a mixture of halogen compounds of different alkaline-earth metals, heating the same until it reaches a state of quiet fusion, pouring the I melted mixture into a mould and allowing the same to cool and solidify, rubbing the solidified mixture on a heated cathode core, thereby applying thereto an adherent coating and r at the same time converting the applied'mixture to a mixture consisting mainly of oxides, 

